1. Field of the Invention
The present invention relates generally to fiber optic networks.
2. Related Art
Today's telecommunication networks employ optical channels to carry traffic between nodes. FIG. 1 is a diagram of a portion of a telecommunication network. FIG. 1 shows optical channel 108 connecting node A with node B, optical channel 116 connecting node A with node D, optical channel 118 connecting node B with node C, and optical channel 126 connecting node C with node D.
Each end of an optical channel is terminated by an opto-electronic line terminating equipment (LTE) or an optical linear terminal (LT) (e.g., an Optical Channel-48 point-to-point line terminating equipment) for converting and multiplexing electrical signals into an optical signal for transmission over an optical channel and for converting a received optical signal into electrical signals for transport over the non-optical portions of the telecommunications network.
For example, linear terminal 106 is connected to one end of optical channel 108 and linear terminal 112 is connected to the other end of optical channel 108. Linear terminal 106 receives electrical signals from electrical digital cross-connect switch (DXC) 102 and transforms those signals into optical signals for transmission over optical channel 108. Linear terminal 112 receives optical signals from optical channel 108 and transforms those optical signals back to the electrical domain.
When there is a break in an optical channel, the linear terminals connected to the optical channel detect the channel failure by sensing a loss of signal condition, for example. Upon detecting a channel failure, the linear terminals send a failure indication to a network management system (not shown). The network management system then directs DXCs 102, 110, 122, and 130 to re-route traffic to restore the network.
A problem with using electrical digital cross-connect switches to re-route traffic when the network experiences an optical channel failure is the substantial amount of time it takes to perform the network restoration.
One solution is to replace the linear terminals with add-drop multiplexers (ADMs) and create a conventional optical ring network, such as a bidirectional line switched ring (BLSR). This approach reduces the amount of time it takes to perform network restoration to the 100 millisecond range (approximately). However, this approach is expensive because ADMs must be purchased to replace the linear terminals.
A network design is needed that can quickly recover from an optical channel failure without requiring replacement of the linear terminals.